This invention relates to an engine control unit (ECU) for a multi-mode engine, and particularly, but not exclusively to an ECU for a dual fuel engine, and to a multi-mode engine comprising such an ECU.
A multi-mode engine is capable of operating in a plurality of different modes, each mode having a different fuel requirement. In other words, a multi-mode engine is powered by different fuels or combinations of fuels in the different modes.
A dual fuel engine is adapted to operate in two modes. Typically a first mode is a diesel mode in which the engine is fuelled solely by diesel fuel, and a second mode is a gaseous fuel mode in which the engine is fuelled predominantly by a gaseous fuel such as natural gas (methane) which is ignited by a relatively small quantity of diesel.
A dual fuel engine may of course run on different types of fuel. The first fuel could be, for example a biodiesel fuel, synthetic fuel or any number of alternative fuels. Similarly, the second fuel does not have to be methane and could be for example, compressed natural gas, biomethane, ethanol, methanol, or hydrogen to name but a few.
The operation of an engine such as an internal combustion engine on a mixture of a liquid fuel such as diesel, and a gaseous fuel such as methane increases the fuel economy and engine efficiency of the engine, whilst at the same time maintaining low levels of undesirable exhaust emissions. As people generally become more aware of the disastrous effect on the environment and weather of the consumption of hydrocarbon fuels, there is greater need to reduce carbon emissions from vehicles such as heavy goods vehicles. One way in which these emissions can be reduced is by powering such vehicles with dual fuel engines which, for at least some of the time, are fuelled predominantly by methane, for example.
Whilst it is known to manufacture engine systems that are able to operate on both diesel and methane, there are many existing conventional diesel engines which cannot be simply replaced for economic reasons.
There is therefore a need to be able to convert existing internal combustion engines designed to run on, for example, diesel, into dual fuel engines which may run on diesel or methane, or a combination of two or more fuels.
A problem encountered with converting existing engines is that existing diesel engines, particularly of the unit injector or common rail type, are controlled by an electronic ECU. This ECU, known as a diesel ECU, controls the injection of diesel into the engine. The ECU comprises an engine map which is essentially a three-dimensional data array installed by the Original Equipment Manufacturer (OEM) which allows the diesel ECU to determine the amount of diesel to be injected into the engine, and the timing of the injection, depending on various parameters. The amount of diesel injected into the engine provides appropriate energy to the engine, taking into account prevailing conditions.
A known engine system comprises a plurality of sensors which measure a plurality of variables such as:                Accelerator Pedal position;        Intake Manifold pressure;        Engine temperature;        Vehicle speed;        Engine speed;        Engine position;        Oil pressure; and        Fuel pressure.        
The sensors supply the ECU with information relating to these parameters. The engine mapping enables the ECU to determine the required level of fuel injection dependent on these parameters, and also in conjunction with other components with ECUs on the vehicle, such as electronic gearbox control, electronic braking systems, and traction control. Typically component ECUs will share information through a controller area network (CAN), and can have an effect on the final required level of fuel injection.
The diesel ECU instructs each of the injectors of the engine to inject a predetermined amount of diesel into the engine at a predetermined time dependent on the parameters measured, by sending a pulse signal to the injector. The injector is generally controlled by the width of the pulse and therefore pulse width modulation may be used to vary the amount of fuel injected into the engine. The diesel ECU also controls the timing of injection of diesel into the engine by each of the injectors.
If an engine is to be adapted to run in a second mode in which a mixture of diesel and methane is to be used to fuel the engine, the ECU must be adapted to instruct each of the diesel injectors to inject less diesel into the engine when the engine is running in the second mode. In order to enable the ECU to instruct each of the injectors appropriately when the engine is running in the second mode, it has previously been thought necessary to alter the engine map of the ECU.
In other words, when the engine is running in the second mode, less diesel is required to be injected into the engine per unit time than when the engine is running on diesel only.
However, OEMs generally do not provide information about or access to the engine map of the diesel ECU, and it is usually not possible therefore to access fuel maps in existing diesel ECUs.
It is necessary for the diesel ECU to remain active even when the engine is running in the second mode in order that the ECU can continue to control other engine components. It is therefore not possible to completely by-pass the diesel ECU which must continue to operate whenever the engine is running in whichever mode, to maintain built in safety features.